MEPS 354:85-95 (2008)  -  DOI: https://doi.org/10.3354/meps07215

ABSTRACT: To assess the contribution of n-3 essential lipids by heterotrophic protists in the pelagic food webs, we examined the kinetics and efficiency of long-chain n-3 essential fatty acid (LCn-3EFA) production of 2 common heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans, fed an alga (Dunaliella tertiolecta) deficient in both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). D. tertiolecta was rapidly ingested and consumed by the heterotrophic protists. Growth rates ranged from 0.77 to 0.82 and 0.78 to 0.92 d^–1 in O. marina and G. dominans, respectively. LCn-3EFA production in the 2 heterotrophic protists reached the highest levels at the highest protist cell density in the feeding experiments, equivalent to a production of 1.9 ± 0.3 µg EPA and 22.3 ± 6.4 µg DHA by O. marina and 4.7 ± 0.5 µg EPA and 16.5 ± 1.1 µg DHA by G. dominans per mg algal carbon consumed. Both protists contained much higher levels of DHA, a nutrient critical for neural and visual development for marine organisms at higher trophic levels, compared to the good food quality alga Rhodomonas salina. This suggests that the LCn-3EFA contribution by heterotrophic protists to the pelagic food webs is quantitatively significant and may be crucial for the production and recruitment of species at higher trophic levels, particularly at times of blooms dominated by algal species deficient in LCn-3EFAs or when the primary producer standing stock is dominated by pico- and nanoplankton during non-bloom periods.

KEY WORDS: Heterotrophic protists · Algae · Essential fatty acids · Nutrient upgrading · Docosahexaenoic acid · Eicosapentaenoic acid · Phytoplankton-heterotrophic protist interface